Answer:
Sample size = 246 .
Step-by-step explanation:
We are given that Bright Bulb light bulb company is planning a study to assess the average life expectancy of their light bulbs. For this they know;
Standard deviation, = 400 hours Confidence interval = 95%
Margin of error = 50 hours
We know that Margin of error formula is given by;
Margin of Error = where = 5%
50 = 1.96 *
= = 15.68
n = = 245.86 ≈ 246
So, sample size needed will be 246 bulbs.